The present invention relates generally to seafloor topography anomaly analysis and deals more specifically with a computerized sonic method for analyzing in real time or in post processing an anomaly in a seafloor topography mapped by a side scan sonar system.
The analyzation of a topographic representation of a seafloor bottom to identify and locate anomalies or targets on the seafloor is generally a tedious and time consuming task. Although techniques for mapping the topographic features of a seafloor in real time using side scan or side looking sonar equipment, also referred to as a side scan sonar tow fish, is generally well known and understood by those skilled in the art, no apparatus or method is currently available to my knowledge that easily and quickly provides the latitude and longitude or the length, width and height of an identified target as the seafloor is being mapped.
The data required in an anomaly analysis is generally obtained from a topographical representation of the seafloor using manual measuring techniques wherein rulers, ten point dividers, Gerber scales and other manually operated measuring implements are employed to measure relative distances from a reference point printed on the representation. Consequently, the anomaly analysis is routinely performed at a location remote from the actual sonar scanning location and often occurs several days after an area of interest has been mapped. Furthermore, the manual measurement procedure and computation of the relative location of an identified target is often very inaccurate and subsequent attempts to observe and/or retrieve the object associated with an identified anomaly at the computed latitude and longitude can be very time consuming.
One drawback sometimes associated with known anomaly analyses methods is that occasionally it is found during the post processing analyzation process that an area of interest is not adequately mapped and the tow vessel and equipment is required to return to the area at a later time to gather additional information or to remap the seafloor to better identify the suspected anomaly. Sometimes the additional mapping is necessary to help verify or determine among other things, whether a previously identified anomaly represents an object of interest, such as, for example, a sunken ship, lost cargo, etc. or whether the anomaly is merely representative of an irregularity in the seafloor or some other unidentified acoustic interference, such as a school of fish, recorded on the topographic representation as an anomaly.
Another drawback associated with the inability to perform an anomaly analysis in real time is the tow vessel and side scan sonar equipment often remain idle during the period of anomaly analysis. Such vessel and equipment idle periods are costly since a crew is generally required to be on standby in case the vessel is required to return to the location of an identified anomaly for further analysis. Also, seafloor mapping is suspended during these idle periods thus substantially reducing the seafloor area that can be mapped during a given time period.
It would be desirable therefore to have a method for performing a seafloor topographic anomaly analysis substantially simultaneously with the production of the seafloor topographic representation in order to provide the latitude and longitude and if desired, the length, width and height of an identified anomaly as a tow vessel and side scan sonar tow fish move relative to the anomaly.
It would also be desirable to provide a side scan sonar anomaly analysis method wherein a seafloor topographic representation is presented on a conventional strip chart recorder paper or a video display and the coordinates associated with the location of an appearance of an anomaly on such a paper or display are produced using conventional digitizers and methods.
The object of the present invention is therefore, to provide a method for analyzing an anomaly in a seafloor topographic representation which overcomes the aforementioned problems associated with manual measurement methods of anomaly analysis.
It is a further object of the present invention to provide a method for analyzing in real time and on-line an anomaly in a seafloor topographic representation wherein the topographic representation is produced using conventional side scan sonar sensing and recording apparatus and techniques wherein the coordinates of an appearance of an anomaly in the topographic representation is digitized using a sonic digitizer and the coordinates representative of the anomaly location are automatically conditioned to compensate for the relative movement of the tow vessel and the side scan sonar tow fish with respect to a starting reference latitude and longitude.
Another object of the invention is to provide a method for analyzing in real time and on-line an anomaly in a seafloor topographic representation wherein relative changes in the speed and course made good of the tow fish during any given time interval during which an appearance of an anomaly occurs in the representation are automatically taken into account in the determination of the latitude and longtitude of the identified anomaly.
Yet another object of the invention is to provide a method for analyzing offline in post processing an anomaly in a seafloor topographic representation wherein the latitude and longitude position of the tow fish before and after the recorded anomaly appearance are manually inputted and correlated to the position of the side scan sonar tow fish at each position of interest in the seafloor topographic representation along the course of the tow fish.